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FlowController.java
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FlowController.java
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/*
* Copyright 2016 Google LLC
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google LLC nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.google.api.gax.batching;
import com.google.api.core.BetaApi;
import com.google.api.core.InternalApi;
import com.google.api.gax.batching.FlowControlEventStats.FlowControlEvent;
import com.google.common.base.Preconditions;
import com.google.common.base.Stopwatch;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nullable;
/** Provides flow control capability. */
@BetaApi("The surface for batching is not stable yet and may change in the future.")
public class FlowController {
/** Base exception that signals a flow control state. */
public abstract static class FlowControlException extends Exception {
private FlowControlException() {}
}
/**
* Runtime exception that can be used in place of FlowControlException when an unchecked exception
* is required.
*/
@BetaApi
public static class FlowControlRuntimeException extends RuntimeException {
private FlowControlRuntimeException(FlowControlException e) {
super(e);
}
public static FlowControlRuntimeException fromFlowControlException(FlowControlException e) {
return new FlowControlRuntimeException(e);
}
}
/**
* Exception thrown when client-side flow control is enforced based on the maximum number of
* outstanding in-memory elements.
*/
@BetaApi
public static final class MaxOutstandingElementCountReachedException
extends FlowControlException {
private final long currentMaxElementCount;
public MaxOutstandingElementCountReachedException(long currentMaxElementCount) {
this.currentMaxElementCount = currentMaxElementCount;
}
public long getCurrentMaxBatchElementCount() {
return currentMaxElementCount;
}
@Override
public String toString() {
return String.format(
"The maximum number of batch elements: %d have been reached.", currentMaxElementCount);
}
}
/**
* Exception thrown when client-side flow control is enforced based on the maximum number of
* unacknowledged in-memory bytes.
*/
@BetaApi
public static final class MaxOutstandingRequestBytesReachedException
extends FlowControlException {
private final long currentMaxBytes;
public MaxOutstandingRequestBytesReachedException(long currentMaxBytes) {
this.currentMaxBytes = currentMaxBytes;
}
public long getCurrentMaxBatchBytes() {
return currentMaxBytes;
}
@Override
public String toString() {
return String.format(
"The maximum number of batch bytes: %d have been reached.", currentMaxBytes);
}
}
/**
* Enumeration of behaviors that FlowController can use in case the flow control limits are
* exceeded.
*/
@BetaApi
public enum LimitExceededBehavior {
/**
* Throws {@link MaxOutstandingElementCountReachedException} or {@link
* MaxOutstandingRequestBytesReachedException}.
*
* <p>This might be appropriate in interactive scenarios. For example, a web server might catch
* these exceptions and report to the user that the system is overloaded and that the user could
* try again later. It could also be useful in applications that implement custom rate-limiting
* logic.
*/
ThrowException,
/**
* Waits until the request can be made without exceeding the limit.
*
* <p>This might be appropriate in batch-processing, where latencies of individual requests are
* not important.
*/
Block,
/**
* Disables flow-control.
*
* <p>This is provided mainly for debugging and not recommended for production use. Having too
* many requests in-flight might cause RPCs to fail due to congested network or the computer to
* run out of memory due to excessive buffering, etc.
*/
Ignore,
}
@Nullable private final Semaphore64 outstandingElementCount;
@Nullable private final Semaphore64 outstandingByteCount;
@Nullable private final Long maxElementCountLimit;
@Nullable private final Long maxRequestBytesLimit;
@Nullable private final Long minElementCountLimit;
@Nullable private final Long minRequestBytesLimit;
private final LimitExceededBehavior limitExceededBehavior;
private final Object updateLimitLock;
// Threshold to record throttling events. If reserve() takes longer than this threshold, it will
// be recorded as a throttling event.
private static final long RESERVE_FLOW_CONTROL_THRESHOLD_MS = 1;
private final FlowControlEventStats flowControlEventStats;
public FlowController(FlowControlSettings settings) {
// When the FlowController is initialized with FlowControlSettings, flow control limits can't be
// adjusted. min, current, max element count and request bytes are initialized with the max
// values in FlowControlSettings.
this(convertFlowControlSettings(settings));
}
@InternalApi("For google-cloud-java client use only")
public FlowController(DynamicFlowControlSettings settings) {
this.limitExceededBehavior = settings.getLimitExceededBehavior();
this.updateLimitLock = new Object();
this.flowControlEventStats = new FlowControlEventStats();
switch (settings.getLimitExceededBehavior()) {
case ThrowException:
case Block:
break;
case Ignore:
this.maxElementCountLimit = null;
this.maxRequestBytesLimit = null;
this.minElementCountLimit = null;
this.minRequestBytesLimit = null;
this.outstandingElementCount = null;
this.outstandingByteCount = null;
return;
default:
throw new IllegalArgumentException(
"Unknown LimitBehaviour: " + settings.getLimitExceededBehavior());
}
this.maxElementCountLimit = settings.getMaxOutstandingElementCount();
this.minElementCountLimit = settings.getMinOutstandingElementCount();
Long initialElementCountLimit = settings.getInitialOutstandingElementCount();
if (initialElementCountLimit == null) {
outstandingElementCount = null;
} else if (settings.getLimitExceededBehavior() == FlowController.LimitExceededBehavior.Block) {
outstandingElementCount = new BlockingSemaphore(initialElementCountLimit);
} else {
outstandingElementCount = new NonBlockingSemaphore(initialElementCountLimit);
}
this.maxRequestBytesLimit = settings.getMaxOutstandingRequestBytes();
this.minRequestBytesLimit = settings.getMinOutstandingRequestBytes();
Long initialRequestBytesLimit = settings.getInitialOutstandingRequestBytes();
if (initialRequestBytesLimit == null) {
outstandingByteCount = null;
} else if (settings.getLimitExceededBehavior() == FlowController.LimitExceededBehavior.Block) {
outstandingByteCount = new BlockingSemaphore(initialRequestBytesLimit);
} else {
outstandingByteCount = new NonBlockingSemaphore(initialRequestBytesLimit);
}
}
public void reserve(long elements, long bytes) throws FlowControlException {
Preconditions.checkArgument(elements >= 0);
Preconditions.checkArgument(bytes >= 0);
Stopwatch stopwatch = Stopwatch.createStarted();
if (outstandingElementCount != null) {
if (!outstandingElementCount.acquire(elements)) {
MaxOutstandingElementCountReachedException exception =
new MaxOutstandingElementCountReachedException(
outstandingElementCount.getPermitLimit());
flowControlEventStats.recordFlowControlEvent(
FlowControlEvent.createReserveDenied(exception));
throw exception;
}
}
// Always allows to send a request even if it is larger than the flow control limit,
// if it doesn't then it will deadlock the thread.
if (outstandingByteCount != null) {
if (!outstandingByteCount.acquirePartial(bytes)) {
if (outstandingElementCount != null) {
outstandingElementCount.release(elements);
}
MaxOutstandingRequestBytesReachedException exception =
new MaxOutstandingRequestBytesReachedException(outstandingByteCount.getPermitLimit());
flowControlEventStats.recordFlowControlEvent(
FlowControlEvent.createReserveDenied(exception));
throw exception;
}
}
long elapsed = stopwatch.elapsed(TimeUnit.MILLISECONDS);
if (elapsed >= RESERVE_FLOW_CONTROL_THRESHOLD_MS) {
flowControlEventStats.recordFlowControlEvent(FlowControlEvent.createReserveDelayed(elapsed));
}
}
public void release(long elements, long bytes) {
Preconditions.checkArgument(elements >= 0);
Preconditions.checkArgument(bytes >= 0);
if (outstandingElementCount != null) {
outstandingElementCount.release(elements);
}
if (outstandingByteCount != null) {
outstandingByteCount.release(bytes);
}
}
/**
* Increase flow control limits to allow extra elementSteps elements and byteSteps request bytes
* before enforcing flow control.
*/
@InternalApi("For google-cloud-java client use only")
public void increaseThresholds(long elementSteps, long byteSteps) {
Preconditions.checkArgument(elementSteps >= 0);
Preconditions.checkArgument(byteSteps >= 0);
synchronized (updateLimitLock) {
if (outstandingElementCount != null) {
long actualStep =
Math.min(elementSteps, maxElementCountLimit - outstandingElementCount.getPermitLimit());
outstandingElementCount.increasePermitLimit(actualStep);
}
if (outstandingByteCount != null) {
long actualStep =
Math.min(byteSteps, maxRequestBytesLimit - outstandingByteCount.getPermitLimit());
outstandingByteCount.increasePermitLimit(actualStep);
}
}
}
/**
* Decrease flow control limits to allow elementSteps fewer elements and byteSteps fewer request
* bytes before enforcing flow control.
*/
@InternalApi("For google-cloud-java client use only")
public void decreaseThresholds(long elementSteps, long byteSteps) {
Preconditions.checkArgument(elementSteps >= 0);
Preconditions.checkArgument(byteSteps >= 0);
synchronized (updateLimitLock) {
if (outstandingElementCount != null) {
long actualStep =
Math.min(elementSteps, outstandingElementCount.getPermitLimit() - minElementCountLimit);
outstandingElementCount.reducePermitLimit(actualStep);
}
if (outstandingByteCount != null) {
long actualStep =
Math.min(byteSteps, outstandingByteCount.getPermitLimit() - minRequestBytesLimit);
outstandingByteCount.reducePermitLimit(actualStep);
}
}
}
private static DynamicFlowControlSettings convertFlowControlSettings(
FlowControlSettings settings) {
return DynamicFlowControlSettings.newBuilder()
.setInitialOutstandingElementCount(settings.getMaxOutstandingElementCount())
.setMinOutstandingElementCount(settings.getMaxOutstandingElementCount())
.setMaxOutstandingElementCount(settings.getMaxOutstandingElementCount())
.setInitialOutstandingRequestBytes(settings.getMaxOutstandingRequestBytes())
.setMinOutstandingRequestBytes(settings.getMaxOutstandingRequestBytes())
.setMaxOutstandingRequestBytes(settings.getMaxOutstandingRequestBytes())
.setLimitExceededBehavior(settings.getLimitExceededBehavior())
.build();
}
LimitExceededBehavior getLimitExceededBehavior() {
return limitExceededBehavior;
}
@InternalApi("For internal use by google-cloud-java clients only")
@Nullable
public Long getMaxElementCountLimit() {
return maxElementCountLimit;
}
@InternalApi("For internal use by google-cloud-java clients only")
@Nullable
public Long getMaxRequestBytesLimit() {
return maxRequestBytesLimit;
}
@InternalApi("For google-cloud-java client use only")
@Nullable
public Long getMinElementCountLimit() {
return minElementCountLimit;
}
@InternalApi("For google-cloud-java client use only")
@Nullable
public Long getMinRequestBytesLimit() {
return minRequestBytesLimit;
}
@InternalApi("For google-cloud-java client use only")
@Nullable
public Long getCurrentElementCountLimit() {
return outstandingElementCount == null ? null : outstandingElementCount.getPermitLimit();
}
@InternalApi("For google-cloud-java client use only")
@Nullable
public Long getCurrentRequestBytesLimit() {
return outstandingByteCount == null ? null : outstandingByteCount.getPermitLimit();
}
@InternalApi("For google-cloud-java client use only")
public FlowControlEventStats getFlowControlEventStats() {
return flowControlEventStats;
}
}